Quality Analysis of Cord Blood Unit (CBU) Segments at the Bank Correlates with the Post-Thaw Transplant Center Results after Albumin-Dextran Dilution

Background: MSKCC analyses have shown that the infused viable CD34+ cell dose is the critical determinant of neutrophil engraftment after CB transplantation (Purtill et al, Blood 2014). However, currently, CD34+ cell viability can only be obtained on transplant day at unit thaw. Whether testing of the segment attached to the freezing bag at the Bank prior to unit release can predict the post-thaw CBU quality/potency at the transplant center is not established. Methods: We compared the post-thaw results of 68 NCBP CBU, AXP-processed, stored in BioArchive freezers, shipped, and thawed at MSKCC, with their respective segment and pre-cryopreservation data. NCBP has developed methodology to analyze cells from the thawed segment (~100 ul) for CD34+ cell count and percent viability by flow cytometry (7-AAD exclusion using ISHAGE gating), and colony-forming units (CFU) using high resolution digital imaging (Albano et al, ASH 2008). At MSKCC, units were thawed using albumin-dextran dilution, evaluated for CD34+ cell count & viability (4-color flow cytometry using modified ISHAGE gating (Scaradavou et al, BBMT 2010), & CFU assays. Results: At NCBP there was a high correlation between the viable CD34+ cell counts and CFU in pre-cryopreservation and segment data (Table). In the 68 CBU thawed at MSKCC, the average decrease in CD34+ cell viability post-thaw compared to that of the segment was 1.9% (SD:+/- 3.9%; p < 0.001) & ranged -11.0% to +12.0% with the lowest post-thaw CD34+ cell viability being 82% (Figure). Moreover, despite potential differences in laboratories and flow cytometric gating, the number of viable CD34+ cells in the unit post-thaw correlated with both the pre-cryopreservation viable CD34+ counts and the results of the segment (Table). The median viable CD34+ cell recovery (ratio of post-thaw to segment viable CD34+ counts) was 128% (SD:+/-43.2). In contrast, however, post-thaw CFU had weak correlation with pre-cryopreservation and segment values (Table). Conclusions: Testing of CBU segments can accurately measure the potency of the frozen CB products, & segment calculations may even underestimate the post-thaw CBU CD34+ cell content. Although the decrease in post-thaw CBU CD34+ cell viability was statistically significant, this difference was too low to be clinically relevant. The poor correlation between segment and post-thaw CFU likely reflects significant inter-laboratory assay variability. These findings indicate that the processing procedures, cryopreservation technology and thaw/dilution methodology generate high quality units and that testing segment CD34+ cell counts and the percentage of viable cells can predict the post-thaw potency. Whether these findings can be generalized to other CB banks and transplant centers requires further investigation.